Wireless communication system, server and mobile station therefor

ABSTRACT

This invention provides a wireless communication system wherein a network to which a mobile station should be handed over can be selected, using parametric data collected from network components other than the mobile station. Time taken for a handover between different types of network systems is reduced. The wireless communication system of the present invention comprises a mobile station equipped with multiple wireless interfaces, a server connected to a fixed network, and multiple access points. The mobile station determines available wireless interfaces and sends notification of the available interfaces&#39; identifiers to the server. The server collects managerial data from network components and selects a wireless interface, based on the notification from the mobile station and the managerial data. The mobile station registers its locations in visiting networks corresponding to multiple available wireless interfaces with the server. The server retains the registrations of mobile station locations for the above wireless interfaces.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a Continuation Application of U.S. application Ser.No. 10/883,785 filed on Jul. 6, 2004 now U.S. Pat. No. 7,610,049. Thepresent application claims priority from U.S. application Ser. No.10/883,785 filed on Jul. 6, 2004, which claims priority from Japanesepatent application 2003-398393 filed Nov. 28, 2003, the entiredisclosure of which is hereby incorporated by reference.

FIELD OF THE INVENTION

The present invention relates to a handover technique between wirelesssystems.

BACKGROUND OF THE INVENTION

Handovers between different types of communications systems such asbetween a cellular mobile telephony network and a wireless LAN arecalled vertical handovers and study results thereof have been reportedin papers, a few of which are cited below.

In one paper, for example, J. Inouye, J. Binkley, J. Watpole, “DynamicNetwork Reconfiguration Support for Mobile Computers,” Proceedings ofACM/IEEE International Conference on Mobile Computing and Networking(Mobicom'97), Budapest, September 1997 (Non-patent document 1), anexample of a networks system where a mobile host adaptively changes overbetween its network interfaces and transmission routes is discussed.According to this paper, an experiment using this networks systemrevealed that, when the mobile host changes over between an interfacefor a wired LAN and an interface for a wireless LAN, for example, itsInternet Protocol (IP) address changes as the interface changes, andconsequently, an application such as telnet cannot be continued. If, forexample, the mobile station performs path rerouting from the wired LANto the wireless LAN, it has to release a communication path set up,using its IP address within the wired LAN, and reconnect to the wirelessLAN, using its IP address within the wireless LAN. The mobile stationhas to re-execute all applications running on it for new connection.

In another paper, for example, Marc Bechler, Hartmut Ritter, “A flexibleMultiplexing Mechanism for Supporting Quality of Service in MobileEnvironments,” Proceedings of the Hawaii International Conference onSystem Science, Maui, Hi., January 2001 (Non-patent document 2),examples of carrying out handovers between different types ofcommunication systems such as between a wireless LAN and a cellularmobile telephony network, using Mobile IP technology, are discussed. Inthese examples, an IP packet into which an application's data ispackaged for transmission to a particular destination is encapsulatedinto an IP packet with the IP address of a selected network device andthen transmitted via the network device to the destination. Because theIP address of the IP packet of the application's data is unchanged, theapplication can continue while the handover takes place.

FIG. 1 shows an example of conventional wireless system architectureusing the Mobile IP technology. Reference numeral 1 denotes a contentsserver, 2 denotes an IP network, 3 denotes a home agent of Mobile IP,and 8 denotes a mobile station. Reference numeral 4 denotes a foreignagent in a wireless LAN network, 5 denotes the wireless LAN networkestablished by a wireless LAN service provider, and 9, 10, and 11 denoteaccess points of the wireless LAN. Reference numeral 6 denotes a foreignagent in a 1xEvDO (cellular mobile telephony system) network, 7 denotesthe 1xEvDO network established by a 1xEvDO service provider, and 12, 13,and 14 are access points of the 1xEvDO. Reference numeral 15 denotes afixed network. Communication from the home agent to a foreign agent isperformed through an “IP tunnel” formed by encapsulating an IP packetwithin an IP packet. The address of the end point of the IP tunnel is aCare-of address. A home address is an IP address assigned to the mobilestation 8, which is independent of where the mobile station 8 is locatedand attached to the Internet. IP packets transmitted to the home addressof the mobile station 8 are intercepted by the home agent and thenforwarded to the Care-of address. The IP tunnel may be terminated at themobile station 8 itself. The foreign agent or the mobile station 8itself at the end point of the IP tunnel receives encapsulated datagramsand the foreign agent forwards decapsulated IP packets to the mobilestation 8.

FIG. 2 illustrates an example of exchanging messages for a handover ofthe mobile station (MS) 8 in the system of FIG. 1. If the mobile station8 is handed over from a wireless LAN access point to a 1xEvDO accesspoint, the Source FA 16 is a foreign agent 4 in the wireless LAN systemand the Target FA 17 is a foreign agent 6 in the 1xEvDO system. If themobile station 8 is handed over from a 1xEvDO access point to a wirelessLAN access point, the Source FA 16 is a foreign agent 6 in the 1xEvDOsystem and the Target FA 17 is a foreign agent 4 in the wireless LANsystem. Assume that the mobile station 8 is downloading contents 20 fromthe contents server 1 via the foreign agent 16. When the mobile station8 detects a new communication system and determines to perform ahandover to that system, it transmits an Agent Solicitation 21 forreceipt by any nearby foreign agent within the subnet of the new systemto solicit transmission of an Agent Advertisement message. The foreignagent 17 transmits an Agent Advertisement 22 to announce its serviceover the subnet and, when the mobile station 8 receives this message, itdetermines in which network it is attached. Even when not receiving theAgent Solicitation 21, the foreign agent 17 periodically broadcasts theAgent Advertisement 22 over the subnet. The mobile station 8 transmits aRegistration Request 23, 24 via the foreign agent 17 to the home agent 3as a message to register its location with the home agent 3. TheRegistration Request 23 message includes the home address of the mobilestation 8, the home agent address, and the address, care-of address ofthe foreign agent 17. Having received the Registration Request 23message, the home agent 3 registers the care-of address of the mobilestation 8 into a forwarded-to-address table. The home agent 3 transmitsback a Registration Response 25 as a message to return the result of themobile station's location registration to the foreign agent 17. Theforeign agent 17 transmits back a Registration Response 26 as a messageto return the result of the mobile station's location registration tothe mobile station 8. The home agent 3 forwards contents 27 via theforeign agent 17. The foreign agent 17 receives IP encapsulated packetsand delivers decapsulated IP payloads to the mobile station 8. Handovertime depends on timing when the mobile station 8 receives the AgentAdvertisement 22 and time required for rerouting on the IP layer is afew seconds.

FIG. 15 shows an encapsulation format example conforming to the IPencapsulation method as specified in RFC2003. The home agent 3encapsulates an IP packet 151 consisting of an IP header 152 and an IPpayload 153, as an IP payload 157, within an IP packet 155. In the IPheader 152, the source address is the IP address of the contents server1 and the destination address is the home address of the mobile station8. In the IP header 156, the source address is the IP address of thehome agent 3 and the destination address is the care-of address of themobile station 8.

Because the encapsulation method in the above example encapsulates an IPpacket within another IP packet, control information increases by theadditional IP header and information transmission efficiency decreases.To reduce the increase in control information, another encapsulationmethod has been proposed as an Internet standard's track protocol. FIG.14 shows an encapsulation format example conforming to the encapsulationmethod as specified in RFC2004. The home agent 3 constructs an IP packet161 by adding an IP header 162 and an address 163 to the IP payload 153of an IP packet 151. In the IP header 162, the source address is the IPaddress of the home agent 3 and the destination address of the care-ofaddress of the mobile station 8. The address 163 is the home address ofthe mobile station 9 and a minimum of 12 bytes of information is added.

[Non-patent document 1] J. Inouye, J. Binkley, J. Watpole, “DynamicNetwork Reconfiguration Support for Mobile Computers,” Proceedings ofACM/IEEE International Conference on Mobile Computing and Networking(Mobicom '97), Budapest, September 1997

[Non-patent document 2] Marc Bechler, Hartmut Ritter, “A flexibleMultiplexing Mechanism for Supporting Quality of Service in MobileEnvironments,” Proceedings of the Hawaii International Conference onSystem Science, Maui, Hi., January 2001

SUMMARY OF THE INVENTION

When a system to which a mobile station should be handed over isdetermined, using measurements data only obtained by the mobile station,a system that is not optimal in terms of efficiency of resources usagemay be selected and its possibility is high. For example, even if thestrength of radio signals received from an access point that is apossible handover candidate is sufficiently strong, if user connectionsto the access point are locally increased, then the communication rateper user will decrease. One object of the present invention is toprovide a handover method in which an optimal system to which a mobilestation should be handed over is determined, using more amount ofparametric data obtained from the whole network, such as the number ofusers per access point.

Through consideration of the conditions that it takes in the order ofseconds for rerouting on the IP layer, another object of the presentinvention is to realize faster rerouting of an IP packet transmissionpath.

Furthermore, high security authentication is generally heavy processing.Such authentication processing that is assumed to be performed each timeof rerouting imposes a large load on the system in question and consumestime. For example, according to a typical authentication protocol,IEEE802.1x, it takes in the order of seconds to complete oneauthentication process. Yet another object of the present invention isto provide a faster handover method taking authentication intoconsideration.

One aspect of the present invention resides in a wireless communicationsystem comprising a mobile station equipped with a plurality of wirelessinterfaces, a server connected to a network, and a plurality of accesspoints. The invention primarily presupposes that the plurality ofwireless interfaces are different types such as wireless LAN and 1xEvDO;however, these interfaces may be same type. Given that the plurality ofwireless interfaces are same type, the mobile station has a plurality ofwireless interfaces of same type. The wireless interfaces may be othertypes than wireless LAN and 1xEvDO. For example, the types of thewireless may involve W-CDMA, CDMA 2000 1x, PHS, UWB, and Bluetooth. Themobile station determines available wireless interfaces and sendsnotification of the available interfaces' identifiers to the server. Themobile station also transmits a handover request message to execute ahandover to another one of the plurality of wireless interfaces to theserver. The server collects managerial data from components of thenetwork and selects a wireless interface to be used for communicationwith the mobile station, based on the notification from the mobilestation and the managerial data. Also, the server sends notification ofthe selected wireless interface's identifier to the mobile station andcontrols packet transmission path routing, based on the handover requestmessage from the mobile station.

In the present invention, the network components are, for example theaccess points and the managerial data comprises the identifiers of thewireless interfaces accommodated by the access points and the radioconditions of the wireless interfaces accommodated by the access points.The server selects, for example, a wireless interface operating at thehighest throughput from the wireless interfaces conforming to differentstandards as the wireless interface to be used for communication.

Another aspect of the present invention resides in a wirelesscommunication system including a mobile station equipped with aplurality of wireless interfaces and a server connected to a network.The mobile station determines available wireless interfaces andregisters its locations in visiting networks corresponding to theplurality of available wireless interfaces with the server. Also, themobile station transmits a handover request message to execute ahandover to any of the wireless interfaces to the server. The serverretains the registrations of the mobile station locations for theplurality of available wireless interfaces. Furthermore, the servercontrols transmission path routing to forward packets to any one of theavailable wireless interfaces, based on the handover request message.The registrations of the mobile station locations are Mobile IPcompliant registrations of the locations.

Still another aspect of the present invention resides in a wirelesscommunication system including a mobile station equipped with aplurality of wireless interfaces and a plurality of access points. Basedon either the authenticated status or the type of authentication foreach of the wireless interfaces, a wireless interface to which themobile station should be handed over is selected.

Means for selecting the wireless interface, for example, preferentiallyselects an authenticated wireless interface rather than anunauthenticated wireless interface. Or the above means, for example,preferentially selects a wireless interface that it takes a short timeto authenticate rather than a wireless interface that it takes a longtime to authenticate.

In the wireless communication system of the present invention, themobile station determines available wireless interfaces and sendsnotification of the available interfaces' identifiers to the server. Theserver collects managerial data from components of the network andselects a wireless interface, based on the notification from the mobilestation and the managerial data. Therefore, by using the combination ofthe data from the mobile station and the data collected from the networkcomponents, an optimal wireless interface to which the mobile stationshould be handed over can be selected.

Also, the server sends notification of the selected wireless interface'sidentifier to the mobile station and controls packet transmission pathrouting, based on the handover request message from the mobile station.Therefore, the mobile station can make its decision to execute ahandover, and the result of the selection of the wireless interface madeby the server may be reflected to this decision.

The mobile station also transmits a handover request message to executea handover to any of the plurality of wireless interfaces to the server.Even if the mobile station makes a handover decision, the mobile stationcan actively initiate the handover procedure and it is detected that thecommunication via the wireless interface to which the mobile station isnow connecting is disconnected. Even if the mobile station makes ahandover decision, an increase in traffic and transmission delay can bereduced with respect to the case where all necessary information istransmitted to the server and a handover decision is made.

The server of the present invention selects, for example, a wirelessinterface operating at the highest data rate from the wirelessinterfaces conforming to different standards as the wireless interfaceto which the mobile station should be handed over. Therefore, thehandover to a system operating at a high transmission rate can beperformed more exactly with respect to the case where a handover isperformed, according to only the radio conditions of wireless channels.The throughput between the mobile station and the fixed network isenhanced and a service that places less load on the mobile station canbe provided. Because traffic can be distributed by deselecting acongested system, the efficiency of usage of wireless resources isenhanced.

The mobile station of the present invention determines availablewireless interfaces and registers its locations in visiting networkscorresponding to the plurality of available wireless interfaces with theserver. Also, the mobile station transmits a handover request message toexecute a handover to any of the wireless interfaces to the server. Theserver retains the registrations of the mobile station locations for theplurality of available wireless interfaces. Furthermore, the servercontrols transmission path routing to forward packets to any one of theavailable wireless interfaces, based on the handover request message.The registrations of the mobile station locations are Mobile IPcompliant registrations of the locations. Therefore, the mobile stationcan register its locations associated with the plurality of availablewireless interfaces prior to a handover. Because the procedure requiredfor packet transmission path rerouting after the mobile station makes ahandover decision can be curtailed, the rerouting time can be shortened.

Furthermore, in the wireless communication system of the presentinvention, a wireless interface to which the mobile station should behanded over is selected, based on either the authenticated status or thetype of authentication for each of the wireless interfaces.

When a wireless interface to which the mobile station should be handedover is selected, for example, an authenticated wireless interface ispreferentially selected rather than an unauthenticated wirelessinterface. Or, for example, a wireless interface that it takes a shorttime to authenticate is preferentially selected rather than a wirelessinterface that it takes a long time to authenticate. Therefore, awireless interface that it takes shorter to authenticate can be selectedpreferentially as the one to which the mobile station should be handedover, and as a result, the handover time can be shortened.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing an example of wireless system architecture;

FIG. 2 illustrates an example of a mobile station location registrationprocedure according to prior art;

FIG. 3 illustrates an example of a handover procedure according to thepresent invention;

FIG. 4 shows a message format example according to the presentinvention;

FIG. 5 shows a message format example according to the presentinvention;

FIG. 6 shows a message format example according to the presentinvention;

FIG. 7 shows a mobile station configuration example according to thepresent invention;

FIG. 8 shows a server configuration example according to the presentinvention;

FIG. 9 shows an example of a table stored on the server in accordancewith the present invention;

FIG. 10 shows an example of a table stored on the server in accordancewith the present invention;

FIG. 11 shows an example of a table stored on the server in accordancewith the present invention;

FIG. 12 shows a message format example according to the presentinvention;

FIG. 13 shows an example of a table stored on the server in accordancewith the present invention;

FIG. 14 shows a packet encapsulation format example conforming to aconventional encapsulation method;

FIG. 15 shows a packet encapsulation format example conforming to aconventional encapsulation method;

FIG. 16 shows a foreign agent configuration example according to thepresent invention;

FIG. 17 shows a conventional packet format example;

FIG. 18 shows an example of a table stored on the server in accordancewith the present invention; and

FIG. 19 illustrates an example of exchanging messages for a mobilestation handover according to prior art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 3 illustrates an example of exchanging messages for a mobilestation 8 handover according to the present invention. The handover isassumed to be performed, for instance, in the wireless systemarchitecture shown in FIG. 1. In FIG. 3, if the mobile station 8 ishanded over from a wireless LAN access point to a 1xEvDO access point,the Source FA 16 is a foreign agent 4 in the wireless LAN and the TargetFA 17 is a foreign agent 6 in the 1xEvDO system. If the mobile station 8is handed over from a 1xEvDO access point to a wireless LAN accesspoint, the Source FA 16 is a foreign agent 6 and the Target FA 17 is aforeign agent 4.

When the mobile station 8 detects system 1 and determines that thesystem 1 is available, the mobile station 8 registers its location withthe home agent 3 through exchange of messages 31, 32, 33, 34, 35, and36. The mobile station determines that the system 1 is available, forexample, if the strength of radio signals that the mobile station 8receives from an access point of the system 1 exceeds a threshold valueor if the mobile station receives a beacon signal transmitted by anaccess point. Or the mobile station may determine so if it has detectedthat an error ratio of data is equal to or less than a predeterminedvalue by checking a CRC or similar code included in every packet thatthe mobile station received from an access point in the system 1. Themobile station 8 retains the number of systems determined available andthe system identifier or the systems' identifiers and transmits anAvailability indication 37 to the home agent 3 to notify the home agentof the number of systems determined available and the system identifieror the systems' identifiers. Here, the system identifier is, forexample, the MAC address of a wireless interface. In the situation whereonly the system 1 is available, the home agent 3 forwards contents 38via the foreign agent 16 to the mobile station 8.

When the mobile station 8 detects system 2 and determines that thesystem 2 is available, the mobile station 8 registers its location withthe home agent 3 through the foreign agent 17 through exchange ofmessages 39, 40, 41, 42, 43, and 44. To notify the home agent 3 that thefirst and second systems are available and of the identifiers of thesesystems, the mobile station 8 transmits an Availability indication 45 tothe home agent 3 through the system 1. The mobile station 8 iscommunicating with the contents server 1, using one of the plurality ofsystems with which its location has been registered. From the contentsserver, no packets are sent to a system with which the mobile stationlocation has been registered, but which is now out of service, and thissystem stands by for serving the mobile station after a handover to itthat may occur later. The home agent 3 continues to forward contents 46via the foreign agent 16 to the mobile station 8.

In the situation where the plurality of systems are available, the homeagent 3 determines an optimal system to which the mobile station shouldbe handed over and recommends the mobile station 8 a handover bytransmitting a Handover recommend 47 to the mobile station. If themobile station 8 determines to execute a handover from the system 1 tothe system 2, then the mobile station 8 transmits a Handover request 48to the home agent 3. If the mobile station 8 determines not to executethe handover, even upon receiving the Handover recommend 47, the mobilestation 8 does not transmit the Handover request 48. In response to theHandover request 48, the home agent 3 reroutes the packet transmissionpath from the route via the foreign agent 16 to an alternative route viathe foreign agent 17. The home agent 3 forwards contents 49 via theforeign agent 17 and through the system 2 to the mobile station 8.

The home agent 3 notifies the mobile station 8 of an optimal system towhich the mobile station should be handed over by the Handover recommend47; instead, the mobile station may obtain this information in such away that, in response to a request from the mobile station, the homeagent 3 transmits this information to the mobile station. In this case,for example, it may be preferable that the mobile station periodicallyreceives the information equivalent to the Handover recommend 47.However, the manner of the notification in which the home agent 3 sendsthe mobile station the Handover recommend 47 involves less delay,because the optimal system notification is sent to the mobile stationjust when a handover becomes advisable as circumstances demand, andavoids redundant periodical sending of same information.

The mobile station 8 owned by a user who is charged for a packet feefinally decides whether or not to connect to the system recommended bythe Handover recommend 47. If connecting to the system, the mobilestation 8 transmits the Handover request. To save the user the troubleof input operation and prevent missing an opportunity of connection, thehandover-related operation of the mobile station can be facilitated sothat the user may not make the decision to connect to the recommendedsystem and perform input operation whenever receiving the Handoverrecommend 47. This may be done, for example, in the following manner:the user may enter a policy (such as, for example, preferentially usingthe wireless LAN system for IP packet communication) to the mobilestation 8 beforehand so that the control unit of the mobile station 8determines to execute a handover in accordance with the policy andautomatically transmits the Handover request 48.

The mobile station 8 may execute the handover passively, triggered bythe Handover recommend 47, or may do actively by transmitting theHandover request 48 by its discretion even if it does not receive theHandover recommend 47. Alternatively, both the mobile station 8 and thehome agent 3 may actively initiate the handover execution. For example,the mobile station 8 makes the decision to execute a handover, using arapidly changing parameter such as radio condition and transmits theHandover request to initiate the handover, whereas the home agent 3determines a system to which the mobile station should be handed over,using a slow changing parameter such as the number of users accommodatedby an access point, and notifies the mobile station of that system bythe Handover recommend. When the mobile station transmits the Handoverrequest 48 to initiate the handover, the identifier of a wirelessinterface to which the mobile station 8 is switching is specified in theHandover request 48 and this interface is referred to as an in-servicemedium. Or, if only one system is available for the mobile station 8,the identifier of the available system's wireless interface of themobile station 8 is also referred to as the in-service medium. Forexample, in FIG. 3, when the mobile station 8 transmits the Availabilityindication 37, only the system 1 is available for the mobile station 8.At this point of time, the identifier of the system 1 wireless interfaceof the mobile station 8 is the in-service medium. Even if the in-servicemedium is determined, communication condition depends on the presence ofdatagrams to be transmitted and packet communication is not alwaysperformed by way of the in-service medium.

FIG. 19 illustrates an example of exchanging messages for a mobilestation 8 handover according to prior art. The handover is assumed to beperformed, for instance, in the wireless system architecture shown inFIG. 1. In FIG. 19, if the mobile station 8 is handed over from awireless LAN access point to a 1xEvDO access point, the Source FA 16 isa foreign agent 4 in the wireless LAN and the Target FA 17 is a foreignagent 6 in the 1xEvDO system. If the mobile station 8 is handed overfrom a 1xEvDO access point to a wireless LAN access point, the Source FA16 is a foreign agent 6 and the Target FA 17 is a foreign agent 4.

When the mobile station 8 detects system 1 and determines that thesystem 1 is available, the mobile station 8 registers its location withthe home agent 3 through exchange of messages 31, 32, 33, 34, 35, and36. The mobile station determines that the system 1 is available, forexample, if the strength of radio signals that the mobile station 8receives from an access point of the system 1 exceeds a threshold valueor if the mobile station receives a beacon signal transmitted by anaccess point. Or the mobile station may determine so if it has detectedthat an error ratio of data is equal to or less than a predeterminedvalue by checking a CRC or similar code included in every packet thatthe mobile station received from an access point in the system 1.

The mobile station 8 communicates with the contents server 1 via theSource FA 16 in the system with which its location has been registered.The home agent 3 continues to forward contents 38 via the foreign agent16 to the mobile station 8.

When the mobile station 8 detects system 2 and determines that thesystem 2 is available, the mobile station 8 registers its location withthe home agent 3 through the foreign agent 17 through exchange ofmessages 39, 40, 41, 42, 43, and 44. The home agent 3 reroutes thepacket transmission path from the route via the foreign agent 16 to analternative route via the foreign agent 17. The home agent 3 forwardscontents 49 via the foreign agent 17 and through the system 2 to themobile station 8.

In the prior art method, when a need for handover arises ascommunication condition changes, the mobile terminal makes a decision toexecute a handover and then the messages 39, 40, 41, 42, 43, and 44 areexchanged between the mobile station 8 and the home agent 3 for mobilestation location registration, followed by packet transmission pathrerouting.

On the other hand, in the present invention, each time the mobileterminal detects an available system, its location is registered(through the messages 31-16 and 39-44) and the home agent 3 is notifiedbeforehand of information about available systems (through the messages37 and 45), and thus the home agent 3 acquires beforehand informationabout the systems to which the mobile station can be handed over.Accordingly, when a need for handover arises, a handover procedure canbe executed through exchange of the Handover recommend 47 and Handoverrequest 48 messages and the like. Therefore, after the mobile terminalmakes the handover decision, the packet transmission path can bererouted substantially in a round-trip time of the messages 47 and 48.Or, in the present invention, after the mobile terminal makes thehandover decision, the packet transmission path can be reroutedsubstantially in the time taken for transmission of the message 48.Because the handover method of the present invention can cut the timerequired for mobile terminal location registration, typically a fewseconds, the handover or rerouting time can be reduced to typically afew hundred milliseconds, substantially equivalent to the round-triptime of the above messages.

FIG. 4 shows a message format of the Availability indication 37, 45.Field, Type 51 contains a code indicating that the message isAvailability indication. Field, MS host ID 52 contains a uniquelyassigned identifier of the mobile station 8 within the system shown inFIG. 1. Field, In-service Medium 53 contains the identifier (MACaddress) of a wireless interface that the mobile station 8 is now using.Field, Number of Media 54 contains the number of available systems withwhich the mobile station 8 has registered its location. In addition,this message includes the following data items 55, 56, 57, 58, and 59that are as many as the number specified in the number of media 54field. Field, Medium Type 55 includes at least a value representing thetype (wireless LAN, 1xEvDO, etc.) of system 1. Field, MAC Address 56includes at least the MAC address of the system 1 interface of themobile station 8. Field, AP Address 57 includes at least the MAC addressof a system 1 access point to which the mobile station 8 is connecting.Field, Home Address 58 includes at least the home address of the mobilestation 8 in the system 1. Field, Care-of address 59 includes at leastthe care-of address of the mobile station 8 in the system 1. The care-ofaddress 59 is included in the Agent Advertisement transmitted by theforeign agent and posted to the mobile station 8. If the system 2 andsubsequent systems are available, the above data items 55, 56, 57, 58,and 59 thereof are stored, following those for the system 1, in theabove fields.

After the mobile station 8 registers its location with a system ordetects availability status change of a system, it transmits anAvailability indication to the home agent 3 through the system to whichit is now connecting. When the mobile station 8 detects that a systemhas become unavailable, it t sends the home agent 3 an Availabilityindication message in which the number of media 54 is decremented by 1and the data items for the unavailable system are removed. If the mobilestation 8 becomes unable to continue communication using the in-servicemedia due to status change, the mobile station 8 selects a system towhich it should be handed over from the available systems and transmitsa Handover request to the home agent, using the wireless interface of anavailable system. In response to the Handover request 48, the home agent3 reroutes the packet transmission path. Then, the mobile station 8transmits an Availability indication that reflects the systemavailability status change to the home agent 3. The mobile station 8sends the home agent the Availability indication message in which thein-service medium field contains the identifier of the wirelessinterface of the system to which it should be handed over, as specifiedin the Handover request, the number of media 54 is decremented by one,and the data items for the unavailable system are removed.

The home agent 3 registers the contents of the Availability indicationmessage into an MS management table. FIG. 9 shows an example of the MSmanagement table. On each row, the following data for a mobile stationis stored. Column, MS host ID 121 stores the identifier of the mobilestation. Column, In-service Medium 121 stores the identifier (MACaddress) of the system that the mobile station is now using. Column,Number of Media 123 stores the number of available systems with whichthe mobile station has registered its location. Column, Media Type 124stores at least the value representing the type (wireless LAN, 1xEvDO,etc.) of system 1 for the mobile station. Column, MAC Address 125 storesat least the MAC address of the system 1 interface of the mobilestation. Column, AP Address 126 stores at least the MAC address of asystem 1 access point to which the mobile station is connecting. Column,Home Address 127 stores at least the home address of the mobile stationin the system 1. Column, Care-of address 128 stores at least the care-ofaddress of the mobile station in the system 1. The above data items 124,125, 126, 127, and 128 as many as the number specified in the number ofmedia 123 column are registered.

The home agent 3 collects network data and registers this data into atable. A protocol for data collection may be, for example, a SimpleNetwork Management Protocol (SNMP) or a particular protocol. As suchdata that the home agent 3 manages, FIG. 10 shows an example of datacollected from the access points of the wireless LAN system and FIG. 11shows an example of data collected from the access points of the 1xEvDOsystem. In the table of FIG. 10, on each row, the following data for awireless LAN access point is stored. Column 101 stores the identifier(MAC address) of the wireless LAN access point. Columns 102, 103, 104,and so on respectively store the identifiers (MAC addresses) of thewireless LAN interfaces of the mobile stations that the access pointaccommodates. Column 105, 106, 107, and so on respectively store radiosignal strength values measured at the access point for the radiosignals from each mobile station. For example, in FIG. 10, an accesspoint with the identifier of AP ID W1 accommodates mobile stations MS IDW11, MS ID W12, MS ID W13, etc. and the measured values of the strengthof received signals from these mobile stations, namely, Received SignalStrength Indicator (RSSI) are RSSI W11, RSSI W12, RSSI W13, etc. Thetable may have an additional column for the number of mobile stationsaccommodated by each access point.

Likewise, in the table of FIG. 11, on each row, the following data for a1xEvDO access point is stored. Column 111 stores the identifier (MACaddress) of the 1xEvDO access point. Columns 112, 113, 114, and so onrespectively store the identifiers (MAC addresses) of the 1xEvDOinterfaces of the mobile stations that the access point accommodates.For example, in FIG. 11, an access point with the identifier of AP ID E1accommodates mobile stations MS ID E11, MS ID E12, MS ID E13, etc. andthe carrier-to-interference ratio (C/I) values for radio signals fromthese mobile stations are C/I E11, C/I E12, C/I E13, etc. The table mayhave an additional column for the number of mobile stations accommodatedby each access point.

When the home agent 3 receives an Availability indication message from amobile station, it refers to the table of FIG. 10 or FIG. 11 for themedium type 55 specified in the message and can look up the data for theaccess point to which the mobile station 8 is connecting. For example,the home agent 3 looks up an access point specified in the AP address 57field of the message from the column 101 or 111 of the table and canknow the identifiers of the mobile stations 112, 113, 114, etc. that theaccess point accommodates or the number of mobile stations accommodatedfrom the column for the number of mobile stations accommodated by eachaccess point if this column exists. For example, assume that, from theidentifiers of the mobile stations 112, 113, 114, etc. that the accesspoint accommodates, the home agent 3 finds one 112 that matches with aMAC address 56 specified in the Availability indication message. Byreferring to the measured value 115 for the mobile station identifier112, the home agent can know the quality (for example, received signalstrength) of a communication channel from the mobile station 8 at theaccess point to which the mobile station 8 that transmitted theAvailability indication is connecting.

FIG. 7 shows a configuration example of the mobile station 8 accordingto the present invention. A control unit 142 exerts control overcomponents 141, 143, 144, 145, and 146 and transmitting and receivingthe messages mentioned in FIG. 3 and other processing. The control unit142 determines whether a wireless LAN interface 145 and a 1xEvDOinterface 146 can be put in service from the conditions of communicationchannels between the mobile station and the access points of eachsystem. A storage unit stores control data for the control unit 142,data entered via a UIF unit 144, and data input through the interfaces145 and 146. The UIF unit 144 consists of user interface devices such asa keyboard, display, etc. The wireless LAN interface 145 sends andreceives data to/from the wireless LAN access points 9, 10, 11. The1xEvDO interface 146 sends and receives data to/from the 1xEvDO accesspoints 12, 13, 14. In an Availability indication message, the MACaddress of the wireless LAN interface 145 or 1xEvDO interface 146 isstored in the MAC address 56 field associated with medium type 55 and APaddress 57 in a set of data items for an available system detected.Although the mobile station is equipped with the two interfaces,wireless LAN interface 145 and 1xEvDO interface 146, is shown by way ofexample in FIG. 7, the mobile station 8 may be equipped with three ormore wireless interfaces.

FIG. 8 shows a configuration example of a server as the home agent 3according to the present invention. A control unit 131 exerts controlover components 132, 134, 133, table data entry and search, transmittingand receiving the messages mentioned in FIG. 3, and other processing. Astorage unit 132 stores the tables that are shown in FIGS. 11, 12, and13. A UIF unit 133 consists of user interface devices such as akeyboard, display, etc. An NW IF unit 134 is a network interface for thehome agent 3 to interface with the IP network. An example of how thehome agent 3 updates the management table will be discussed below. Whenan packet 151 is input to the NW IF unit 134, the control unit 131checks the destination address included in the IP header 152. If thedestination address is the IP address of the home agent 3, the controlunit 131 checks data contained in the IP payload 153. If a given fieldof the IP payload 153 contains the code indicating Availabilityindication, the control unit 131 determines that an Availabilityindication message is stored in the IP payload 153. The control unit 131looks for an MS host ID 52 specified in the Availability indicationmessage from the MS host ID 121 column of the MS management table storedin the storage unit 132. If the MS host ID 52 is not found, the controlunit 131 adds the MS host ID 52 to the MS management table and copiesthe contents of the subsequent fields 53, 54, 55, 56, 57, 58, and 59 ofthe Availability indication message into the corresponding columns 122,123, 124, 125, 126, 127, and 128 on the added row. If the MS host ID 52is found, the control unit 131 copies the contents of the subsequentfields 53, 54, 55, 56, 57, 58, and 59 of the Availability indicationmessage into the corresponding columns 122, 123, 124, 125, 126, 127, and128 on the row of the MS host ID 121.

An example of how the control unit 131 of the home agent 3 determines asystem to which the mobile station should be handed over will bediscussed below. If there are a plurality of available systems, asindicated in the Availability indication message, then the control unit131 determines on optimal system. If the number of available systems isone, the home agent 3 uses the available system. Now assume thatwireless LAN is specified as the first medium type 55 and 1xEvDO as thesecond medium type 55 in the Availability indication message.

In general, a wireless LAN access point allocates data transmission timeslots to mobile stations that it serves by Carrier Sense Multiple Accesswith Collision Avoidance (CSMA/CA) and a 1xEvDO access point does so bytransmission scheduling. It does not happen that only a particularmobile station occupies transmission time slots and, basically, the timeslots are evenly allocated to the mobile stations. Communication timeallocated to one mobile station is considered to be the time divided bythe number of the mobile stations accommodated by the access point.

The data communication rate of a wireless LAN channel varies, dependingon RSSI, and the data communication rate of a 1xEvDO channel varies,depending on C/I, and both are expressed as the functions of RSSI andC/I, respectively. Thus, the wireless LAN and 1xEvDO channel data ratesare represented by DRw(RSSI) and DRe (C/I), respectively.

An effective data rate of a wireless LAN channel is calculated byequation 1 and an effective data rate of a 1xEvDO channel is calculatedby equation 2. In equation 1, Nw is the number of mobile stationsaccommodated by a wireless LAN access point. In equation 2, Ne is thenumber of mobile stations accommodated by a 1xEvDO access point. Nw andNe can be obtained from the tables stored in the storage unit 132. Nowassume that the first MAC address 56 specified in the Availabilityindication 45 message is MS ID W11. First, retrieve a measured value ofRSSI W11 from the table of FIG. 10 and get DRw(RSSI W11). The number ofthe identifiers of the mobile stations including the MS ID W11, 102,103, 104, etc. accommodated by the access point AP ID W1 is Nw. Bydividing DRw(RSSI W11) by Nw, a value of effective data rate Rw of thewireless LAN channel is obtained.

Now assume that the second MAC address 56 specified in the Availabilityindication 45 message is MS ID E21. Retrieve a value of C/I E21 from thetable of FIG. 10 and get DRe (C/I E21). The number of the identifiers ofthe mobile stations including the MS ID E21, 112, 113, 114, etc.accommodated by the access point AP ID E2 is Ne. By dividing DRe(C/IE21) by Ne, a value of effective data rate Re of the 1xEvDO channel isobtained.Rw=DRw(RSSI)/Nw  [Equation 1]Re=DRe(C/I)/Ne  [Equation 2]

The control unit 131 compares the value of Rw calculated by using thefirst MAC address 56 and the value of Re calculated by using the secondMAC address 56 for the mobile station 8 identified by the MS host ID 52in the Availability indication 45 message. The control unit 131determines which system is optimal by which channel is a greatereffective data rate and regards the thus determined system as anin-service medium for the mobile station 8 identified by the MS host ID52. If Re is greater than Rw, the control unit 131 regards 1xEvDO as thein-service medium. If Rw is greater than Re, the control unit 131regards wireless LAN as the in-service medium.

If the system selected in the manner described above differs from thein-service system 122 for the mobile station in the MS management table,the control unit 131 transmits a handover recommend 47 to the mobilestation 8. FIG. 5 shows a message format example of the handoverrecommend. Field, Type 61 contains a code indicating that the message ishandover recommend. Field, MS host ID 62 contains the identifier of themobile station 8 as the destination of the message. Field, In-serviceMedium 63 contains the type of the system that the mobile station 8 isusing. Field, Medium Type 64 contains the type of the recommended systemto which the mobile station should be handed over. Field, MAC Address 65contains the MAC Address of the recommended system to which the mobilestation should be handed over. For example, if the control unit 131 hasselected 1xEvDO as the system to which the mobile station should behanded over, then the control unit 131 creates a handover recommendmessage in which 1xEvDO is set in the medium type 64 field and the MACaddress 56 of the system 2 specified in the Availability indication 45is set in the MAC address 65 field.

If the mobile station 8 accepts the recommended system in the handoverrecommend 47 and determines to execute the handover to that system, themobile station 8 transmits a handover request 48 to the home agent 3.FIG. 6 shows a message format example of the handover request. Field,Type 71 contains a code indicating that the message is handover request.Field, MS host ID 72 contains the identifier of the mobile station 8 asthe source of the message. Field, In-service Medium 73 contains the typeof a wireless interface that the mobile station 8 is now using. Field,Medium Type 74 contains the type of the system to which the mobilestation should be handed over. Field, MAC Address 75 contains the MACaddress of a wireless interface for the system to which the mobilestation should be handed over. Field, Home Address 76 contains the homeaddress of the mobile station 8 associated with the wireless interfacefor the system to which the mobile station should be handed over. Field,Care-of address 77 contains the care-of address of the mobile station 8associated with the wireless interface for the system to which themobile station should be handed over. Upon receiving the handoverrequest, the home agent 3 sets the MAC address 75 to replace the entryfor the mobile station in the in-service medium 122 column of the MSmanagement table.

The contents server 1 transmits packets to the home address of themobile station 8 and the home agent 3 performs packet transmissioncontrol to forward the packets via an optimal system. An example of howthe server as the home agent 3 performs this control. The control unit131 checks the destination address included in the IP header 152 of anIP packet 151 input from contents server 1 to the NW IF unit 134. If thedestination address is any of the home addresses 58 of the mobilestation 8 for a plurality of available systems, the control unit 131encapsulates the IP packet 151.

If the encapsulation method conforming to RFC2003 is applied, thecontrol unit 131 first changes the destination address in the IP header152 to the home address of the mobile station 8 for the in-servicesystem. The home address for the in-service system is obtained in thefollowing way: from the MAC address 125 entries for the plurality ofsystems for the mobile station 8 in the MS management table, look up onethat matches with the in-service system 122 entry and refer to the homeaddress 127 entry for the same system. If the destination address storedin the IP header 152 of the received IP packet 151 matches thedestination address retrieved from the MS management table, the IPheader 152 need not be changed. Moreover, the control unit 131 adds anIP header 156 to the IP packet with its destination address changed. Inthe IP header 156, the IP address of the home agent 3 is specified asthe source address and the care-of address in the in-service system 122is specified as the destination address. The care-of address in thein-service system is obtained in the following way: from the MAC address125 entries for the plurality of systems for the mobile station 8 in theMS management table, look up one that matches with the in-service system122 entry and refer to the care-of address 128 entry for the samesystem. Then, the control unit 131 transmits the thus encapsulated IPpacket through the NW IF unit 134.

If the encapsulation method conforming to RFC2004 is applied, thecontrol unit 131 adds an IP header 162 and an address 163 to the IPpayload 153. The address 163 is the home address of the mobile station 8for the in-service system. The home address for the in-service system isobtained in the following way: from the MAC address 125 entries for theplurality of systems for the mobile station 8 in the MS managementtable, look up one that matches with the in-service system 122 entry andrefer to the home address 127 entry for the same system. In the IPheader 162, the IP address of the home agent is specified as the sourceaddress and the care-of address in the in-service system 122 isspecified as the destination address. The care-of address in thein-service system is obtained in the following way: from the MAC address125 entries for the plurality of systems for the mobile station 8 in theMS management table, look up one that matches with the in-service system122 entry and refer to the care-of address 128 entry for the samesystem. Then, the control unit 131 transmits the thus encapsulated IPpacket through the NW IF unit 134.

The contents server 1 need not know the optimal system for the mobilestation 8. The contents server 1 only transmits packets to the homeaddress of the mobile station 8 and then the home agent 3 performscontrol to forward the packets via the optimal system. In the following,an example of the home agent 3 operations will be discussed; that is,collecting managerial data from foreign agents and selecting a wirelessinterface, based on the data received from the mobile station throughthe above messages and the managerial data. FIG. 16 shows a foreignagent 4 configuration example. An NW IF unit 202 is a network interfacefor the foreign agent to interface with a network 2. An NW IF unit 104is a network interface for the foreign agent 4 to interface with anetwork 5. A control unit 201 performs packet transmission path routing,referring to table data stored in a storage unit 203. The storage unit203 stores tables for packet transmission path routing and statisticsdata for network management. A UIF unit 205 consists of user interfacedevices such as a keyboard, display, etc. Assume that the NW IF units202, 204 are Ethernet® (a registered trademark of Xerox Corporation)adapters compliant with the IEEE802.3 standard.

FIG. 17 shows a packet format example of packets that are input andoutput through the NW IF units 202, 204. Reference numeral 180 denotesan Ethernet® packet, 181 denotes the header part of the Ethernet®packet, and 182 denotes the data part of the Ethernet® packet. Referencenumeral 183 denotes the Frame Check Sequence (FCS) part of the Ethernet®packet, wherein the FCS code is used to detect a packet data error. Theheader part 181 is a control information part including a destinationaddress 185 and a source address 186. The IP packet 151 is stored in thedata part 182.

When the NW IF unit 202 receives a packet 180 from the network 2, thecontrol unit 201 parses the destination address 185. If the destinationaddress 185 is the MAC address of the NW IF unit 202, the control unitchecks the packet 180 data for an error, using the FCS. The control unit201 counts up the number of packets 180 received by the NW IF unit 202and stores the number of received packets into a given register in thestorage unit 203. If the packet 180 data is free from an error, thecontrol unit 201 processes the IP packet 151 stored in the data part182, according to the Internet Protocol. If, for example, the datastored in the data part 182 consists of an encapsulated IP packet 155 or161, the control unit 201 parses the destination address included in theassociated IP header 156 or 162. If the destination address (care-ofaddress) in the IP header 156 or 162 is the IP address of the NW IF unit202 of the foreign agent 4, the control unit 201 decapsulates the IPpacket 151 from the encapsulated IP packet 155 or 161. Then, the controlunit 201 executes transmission path finding to the destination addressof the IP packet 151, referring to, for example, the table for packettransmission path routing stored in the storage unit 132.

If a transmission path from the NW IF unit 204 to the destinationaddress has been found by the path finding, the control unit 201constructs an Ethernet® packet 180 into which the IP packet 151 isstored and transmits that packet through the NW IF unit 204. If the pathfinding result is no path to the destination address of the IP packet151, the control unit 201 discards the IP packet 151. The control unit201 executes transmission path finding to the destination address of theIP packet 155 or 161, referring to the table for packet transmissionpath routing stored in the storage unit 132. If a packet 180 data erroris detected, the control unit 201 counts up the number of packetsincluding errors and stores that number into a given register in thestorage unit 203. The control unit 201 discards packets 180 includingerrors, counts up the number of discarded packets, and stores thatnumber into a given register in the storage unit 203. Moreover, thecontrol unit 201 calculates a packet discard ratio by dividing thenumber of discarded packets by the number of received packets and storesthis ratio into a given register in the storage unit 203.

When the NW IF unit 204 receives a packet 180 from the network 5, thecontrol unit 201 parses the destination address 185. If the destinationaddress 185 is the MAC address of the NW IF unit 204, the control unitchecks the packet 180 data for an error, using the FCS. The control unit201 counts up the number of packets 180 received by the NW IF unit 204and stores the number of received packets into a given register in thestorage unit 203. If the packet 180 data is free from an error, thecontrol unit 201 processes the IP packet 151 stored in the data part182, according to the Internet Protocol.

The control unit 201 executes transmission path finding to thedestination address of the IP packet 151, referring to, for example, thetable for packet transmission path routing stored in the storage unit132. If a transmission path from the NW IF unit 202 to the destinationaddress has been found by the path finding, the control unit 201constructs an Ethernet® packet 180 into which the IP packet 151 isstored and transmits that packet through the NW IF unit 202. If the pathfinding result is no path to the destination address of the IP packet151, the control unit 201 discards the IP packet 151. If a packet 180data error is detected, the control unit 201 counts up the number ofpackets including errors and stores that number into a given register inthe storage unit 203. The control unit 201 discards packets 180including errors, counts up the number of discarded packets, and storesthat number into a given register in the storage unit 203. Moreover, thecontrol unit 201 calculates a packet discard ratio by dividing thenumber of discarded packets by the number of received packets and storesthis ratio into a given register in the storage unit 203.

The home agent 3 collects parametric data of network condition andregisters such data into a table. A protocol for data collection may be,for example, the SNMP or a particular protocol. As such data that thehome agent 3 manages, FIG. 18 shows an example of the table of the datacollected from foreign agents. FIG. 18 is a data table example assumingthat there are a plurality of foreign agents 1 to L. In the table ofFIG. 18, one each row, the following data for a foreign agent is stored.Column 191 stores the identifier of the NW IF unit of the foreign agent(the IP address of the NW IF unit 202). Column, packet error count 192stores the number of packets including errors counted up by the controlunit 201. Column, packet discard ratio 193 stores the packet discardratio calculated by the control unit 201.

An example of how the control unit 131 of the home agent 3 determines asystem to which the mobile station should be handed over will bediscussed below. When the home agent is informed that a plurality ofsystems are available for the mobile station by the Availabilityindication message, it determines an optimal system. If only one systemis available for the mobile station, the home agent 3 uses the availablesystem. Assume that wireless LAN is specified as the first medium type55 and 1xEvDO as the second medium type 55 in the Availabilityindication message that the home agent 3 received most recently. Alsoassume that the in-service medium 53 is wireless LAN. The control unit131 learns the care-of address 59 in the system for which the MACaddress 56 matches with the in-service medium 53 from the Availabilityindication. The thus learned care-of address 59 is the IP address of theforeign agent 4 of the in-service medium. The control unit 131 looks upthe learned care-of address 59 from the foreign agent identifier 191column of the table shown in FIG. 18. When the control unit 131 findsout the foreign agent identifier 191 matched with the learned care-ofaddress 59 from the table, it learns the associated packet discard ratio193. This packet discard ratio 193 is the packet discard ratio on theforeign agent 4. The control unit 131 compares the learned packetdiscard ratio with a threshold value. If the packet discard ratio is notless than a given value, the control unit 131 deselects the system usingthe foreign agent 4, that is, the wireless LAN system.

Now assume that the control unit 131 compares the packet discard ratiowith a threshold value and the packet discard ratio exceeds thethreshold value. Then, the control unit 131 sends the mobile station ahandover recommend 47 message in which a 1xEvDO system type is set inthe medium type 64 field and the MAC address of the 1xEvDO interface isset in the MAC address 65 field. FIG. 5 shows a message format exampleof the handover recommend. Field, Type 61 contains a code indicatingthat the message is handover recommend. Field, MS host ID 62 containsthe identifier of the mobile station 8 as the destination of themessage. Field, In-service Medium 63 contains the type of the systemthat the mobile station 8 is using. Field, Medium Type 64 contains thetype of the recommended system to which the mobile station should behanded over. Field, MAC Address 65 contains the MAC Address of therecommended system to which the mobile station should be handed over.For example, if the control unit 131 has selected 1xEvDO as the systemto which the mobile station should be handed over, then the control unit131 creates a handover recommend message in which 1xEvDO is set in themedium type 64 field and the MAC address 56 of the system 2 specified inthe Availability indication 45 is set in the MAC address 65 field. Ifthe mobile station 8 accepts the recommended system in the handoverrecommend 47 and determines to execute the handover to that system, themobile station 8 transmits a handover request 48 to the home agent 3.Upon receiving the handover request, the home agent 3 reroutes thepacket transmission path from the LAN system to the 1xEvDO system.

While, in the above example, wireless interface selection is made byusing the packet discard ratio as managerial data, packet error count,the number of packets received at network components, and the amount ofdata received per unit time may be used as the managerial data. While,in the above example, the home agents collects the managerial data fromthe foreign agents by way of example of network components, the networkcomponents may include routers, switches, and gateways.

An example of selecting a wireless interface to which the mobile stationshould be handed over, using authenticated status data per wirelessinterface, will be discussed below. FIG. 12 shows a message formatexample of Availability indication 37, 45. Field, Authenticated Status60 contains data indicating that the particular type of wirelessinterface of the mobile station is authenticated by an authenticationserver that the communication service provider operates per availablesystem. Normally, users and mobile stations to receive a service canmake use of communication services only after being authenticated by theservice provider. The authentication server is included in the networkthat the service provider operates, such as, for example, the specifictypes of networks 5 and 7. For example, as per the wireless LAN standard(IEEE 802.11), a mobile station is notified of its authenticated statusby a control signal from an access point. After the mobile station 8registers its location with a system or detects availability statuschange of a system, it transmits an Availability indication to the homeagent 3 through the system to which it is now connecting. In addition tothe above cases, when the mobile station 8 detects authenticated statuschange, it transmits an Availability indication with the authenticatedstatus 60 updated to the home agent 3.

FIG. 13 shows a format example of the MS management table that the homeagent 3 manages. Column, Authenticated Status 139, for example, storesdata indicating that the particular type of wireless interface of eachmobile station, identified by the MAC address 125, is authenticated bythe authentication server that the communication service provideroperates. An example of how the control unit 131 of the home agent 3determines a wireless interface to which the mobile station should behanded over will be discussed below. When the home agent is informedthat a plurality of wireless interfaces are available for the mobilestation by the Availability indication message, it determines an optimalwireless system. If only one wireless interface is available for themobile station, the home agent 3 uses the available wireless interface.Now assume that wireless LAN is specified as the first medium type 55and 1xEvDO as the second medium type 55 in the Availability indicationmessage

The effective data rate Rw of a wireless LAN channel is calculated byequation 3 and the effective data rate Re of a 1xEvDO channel iscalculated by equation 4. In equation 3, Waw is weight by theauthenticated status of the wireless LAN interface. In equation 4, Waeis weight by the authenticated status of the 1xEvDO interface. Thecontrol unit 131 assigns a weight, referring to the authenticated status129 in the MS management table. The weight is positive and anauthenticated interface is assigned a greater weight than that notauthenticated.Rw=DRw(RSSI)*Waw/Nw  [Equation 3]Re=DRe(C/I)*Wae/Ne  [Equation 4]

The control unit 131 calculates Rw and Re, based on the correspondingtwo MAC address 56 entries for the same MS host ID 52 in theAvailability indication message and compares calculated Rw and Re. Thecontrol unit 131 determines which system is optimal by which channel isa greater effective data rate and selects the thus determined system asthe system to which the mobile station 8 identified by the MS host ID 52should be handed over. By using this method, an authenticated wirelessinterface is more likely to be selected and, consequently, thepossibility of a delay due to an authentication process will be reduced.

If the system selected in the manner described above differs from thein-service system 122 for the mobile station in the MS management table,the control unit 131 transmits a handover recommend 47 to the mobilestation 8. If the mobile station 8 accepts the recommended system in thehandover recommend 47 and determines to execute the handover to thatsystem, the mobile station 8 transmits a handover request 48 to the homeagent 3. Upon receiving the handover request, the home agent 3 sets theMAC address 75 to replace the entry for the mobile station in thein-service medium 122 column of the MS management table.

In FIG. 13, for example, the Authenticated Status 129 column may storedata indicating that the particular type of wireless interface of eachmobile station, identified by the MAC address 125, is authenticated bythe authentication server that the communication service provideroperates and data identifying the type of an authentication process. Inthis case as well, the effective data rate Rw of a wireless LAN channelis calculated by equation 3 and the effective data rate Re of a 1xEvDOchannel is calculated by equation 4, as described in the above example.In equation 3, Waw is weight by the authenticated status of the wirelessLAN interface. In equation 4, Wae is weight by the authenticated statusof the 1xEvDO interface. The control unit 131 assigns a weight,referring to the authenticated status 129 in the MS management table.The weight is positive and an authenticated interface is assigned agreater weight than that not authenticated. A type of an authenticationprocess imposing a larger processing load on the network components orrequiring a longer processing time is assigned a smaller weight. Byusing this method, a wireless interface that is authenticated for ashorter time is more likely to be selected and, consequently, thepossibility of a delay due to an authentication process will be reduced.

What is claimed is:
 1. A wireless communication system, comprising: amobile station which includes a first wireless interface correspondingto a first wireless communication protocol and a second wirelessinterface corresponding to a second wireless communication protocol; aserver connected to a network; a first access point coupled to thenetwork and to report according to the first wireless communicationprotocol; and a second access point coupled to the network and to reportaccording to the second wireless communication protocol; wherein thefirst access point reports, to the server, a first communicationinformation of a first wireless communication condition, wherein thefirst wireless communication condition comprises a radio conditionbetween the first access point and the mobile station which has beenaccommodated by the first access point, the mobile station sends, to theserver, a handover request to change communication path of the mobilestation from the second access point to the first access point, theserver determines whether to change communication path of the mobilestation from the second access point to the first access point on thebasis of the first communication information, and if it is determined tochange the communication path from the second access point to the firstaccess point, the server controls packet transmission path routingrelated to the mobile station for handover of the mobile station.
 2. Awireless communication system according to claim 1, wherein: the secondaccess point reports, to the server, a second communication informationof a second wireless communication condition related to the secondwireless communication protocol, wherein the second wirelesscommunication condition comprises a radio condition between the secondaccess point and the mobile station which has been accommodated by thesecond access point, and the server compares between the firstcommunication information and the second communication information todetermine whether to change communication path and sends handoverrecommendation message to the mobile station on the result of thecomparison.
 3. A wireless communication system according to claim 2,wherein the first communication information includes at least one ofpacket discard ratios, packet error counts, a number of packets receivedat the access points, and an amount of data received per unit.
 4. Awireless communication system according to claim 2, wherein the firstcommunication information is related to a communication condition ofcommunication between the first access point and a plurality of mobilestations which are accommodated by the first access point.
 5. A wirelesscommunication system according to claim 2, wherein the secondcommunication information is related to communication condition betweenthe second access point and a plurality of mobile stations which areaccommodated by the second access point.
 6. A wireless communicationsystem according to claim 2, wherein the mobile station receives thehandover recommendation message from the server, and determines whetherto change from the second wireless network interface to the firstwireless network interface on the basis of the handover recommendationmessage.
 7. A wireless communication method in a network systemincluding a first access point to report according to a first wirelesscommunication protocol, a second access point to report according to asecond wireless communication protocol and a server coupled to the firstaccess point and the second access point, the method comprising thesteps of: providing, a mobile station, a first wireless communicationnetwork according to the first wireless communication protocol and asecond wireless communication network according to the second wirelesscommunication protocol; collecting, by the server, a first informationrelated to a condition of the first wireless communication network and asecond information related to a condition of the second wirelesscommunication network; and sending, by the server, to the mobile whichis accommodated by either the first access point or the second accesspoint, a handover recommendation request to recommend handover betweenthe first wireless communication network and the second wirelesscommunication network on the basis of the first information and thesecond information.
 8. A wireless communication method according toclaim 7, further comprising the step of: sending, a handover request, bythe mobile station, to either the first access point or the secondaccess point, wherein the handover request is for handing over themobile station between the first access point and the second accesspoint.
 9. A wireless communication method according to claim 7, whereinif a condition of a wireless network provided by an access point whichhas not accommodated the mobile station is better than that of awireless network provided by an access point which has accommodated themobile station, then the method further comprises the step ofdetermining, by the server, to send a handover recommendation message tothe mobile station.
 10. A mobile station comprising: a first wirelessnetwork interface operably associated with a first wireless network, thefirst wireless network having a first access point coupled to a servervia a network; a second wireless network interface operably associatedwith a second wireless network, the second wireless network having asecond access point coupled to the server via the network; a controlunit which is coupled to the first wireless network interface and thesecond wireless network interface, and which communicates via the firstwireless network interface to the first access point which hasaccommodated the mobile station; wherein the control unit receives ahandover recommendation message from the server via the first wirelessnetwork interface, with response to the handover recommendation message,sending a handover request message via the first wireless networkinterface to the first access point, and, after sending the handoverrequest message, communicates to the second access point whichaccommodates the mobile station via the second wireless networkinterface.
 11. A mobile station according to claim 10, wherein thehandover recommendation message is created by the server on the basis ofresult of comparison between a first wireless network condition and asecond wireless network condition.